1. Field of the Invention
The present invention relates to a method for manufacturing a flexible display device and a flexible display device thereby, and more particularly, to a method for manufacturing a flexible display device in which the stability of the process is enhanced and the production yield is increased.
2. Description of the Related Art
In the display device market, the flat panel display (hereinafter “FPD”) has been remarkably rapidly replacing the CRT (cathode ray tube) monitor. There are many kinds of FDP devices, for example, the liquid crystal display (LCD), the plasma display panel (PDP) and the organic electro-luminescence display (OELD). An FPD has lighter weight and thinner thickness as compared with a CRT. Therefore, an FPD is particularly suitable for a large size display system or a portable display system. Because the main elements of the FPD are formed by high temperature processes, most FPD uses glass substrates to endure against the high temperature required in the manufacturing processes. However, because the glass substrate is rigid at room temperature, the glass substrate cannot be freely applied to a flexible display device. Recently, flexible materials have been used for the FPD to develop flexible display devices such that the displays can be rolled or folded to be freely handled in any conditions. That is, using a flexible material such as plastic film or metal foil, a flexible display will have the same display performance even when it is rolled or bent and, therefore, are of great interest in the display industries.
The currently used flexible substrate materials such as plastic substrates or metal foils have the heat resistances inferior to those of glass substrates. Therefore, these flexible substrates can be easily deformed by the high temperatures applied during the processing steps for manufacturing the display elements. The deformed substrate cannot guarantee the quality of the display elements formed thereon. That is, it is impossible to form the display elements on the flexible substrate directly.
Recently, to overcome the above problem, the substrate transcription method has been suggested. After forming the display elements on a rigid substrate, such as a glass substrate, a flexible substrate is attached to the display elements, and then, the glass (rigid) substrate is removed.
The FIGS. 1A to 1D illustrate a method for manufacturing the flexible display device according to the substrate transcription method according to the related art. The substrate transcription method includes forming an insulating protection layer 3 on a glass substrate 1, forming a display element layer 5, attaching a flexible substrate 7, and removing the glass substrate 1 and the insulating protection layer 3.
In the step of forming the insulating protection layer 3, as shown in FIG. 1A, the insulating protection layer 3 is deposited on a glass substrate 1 with a thickness to have enough thermal resistance against the heat of the manufacturing process. The insulating protection layer 3 is made of a silicon oxide (SiOx) or a silicon nitride (SiNx).
In the step for forming the display element layer 5, as shown in FIG. 1B, various elements (lines, electrodes, thin film transistors, etc) configuring the display elements are formed on the insulating protection layer 3. The step for forming the display element layer 5 includes many photo-lithography processes and etching processes.
In the step for attaching the flexible substrate 7, as shown in FIG. 1C, the flexible substrate 7, such as a thin plastic substrate or a metal foil, is attached on the display element layer 5 by an adhesive. The flexible substrate 7 will be the actual substrate of the display device to support the display element layer 5 while permitting flexibility of the display device.
Finally in the step of removing the glass substrate 1 and the insulating protection layer 3, as shown in FIG. 1D, the glass substrate 1 and the insulating protection layer 3 are removed using an etchant, such as hydrogen fluoride (HF). Further, a polishing method using a grinder, such as alumina, is used after etching the glass substrate 1 for enhancing the etched surface. The polishing method for removing the glass substrate 1 cannot be applied when the size (diagonal length) of the glass substrate 1 is larger than 1 m. When removing the glass substrate 1 having a diagonal length over 1 m, the etching process is only used. Because only the flexible substrate 7 remains on the display element layer 5, the display device is flexible.
As mentioned above, when the etching process is applied to the substrate transcription method, the etchant may intrude into and attack the display element layer 5 while the insulating protection layer 3 is removed. As a result, the stability of the production process and the production yield of the flexible display device are degraded.